Nutrients, Chlorophyll, and Internal Tides in the St. Lawrence Estuary

1976 ◽  
Vol 33 (12) ◽  
pp. 2747-2757 ◽  
Author(s):  
Jean-Claude Therriault ◽  
Guy Lacroix
Keyword(s):  
Surface Waters ◽  
Internal Tides ◽  
Upstream Region ◽  
Mixing Process ◽  
Low Oxygen ◽  
Lawrence Estuary ◽  
Deep Waters ◽  
High Nutrient ◽  
Phosphate Nitrate ◽  
St Lawrence Estuary

Tide-dependent variations of temperature, salinity, dissolved oxygen, phosphate, nitrate, and chlorophyll a support the existence of internal tides (longitudinal and transversal) in the St. Lawrence estuary. Vertical oscillations of the poorly oxygenated and nutrient-rich intermediate and deep waters of the estuary have been documented at the head of the Laurentian Channel, the region in which the internal tides are thought to be generated. Penetration of intermediate waters (high-nutrient and low-oxygen concentrations) beyond the Laurentian Channel associated with the internal tides and linked with an intense mixing process in the upstream region permits the nutrient enrichment of the surface waters and their eventual advection in the seaward direction.

scholarly journals Spatial variations in CO<sub>2</sub> fluxes in the Saguenay Fjord (Quebec, Canada) and results of a water mixing model

2020 ◽  
Vol 17 (2) ◽  
pp. 547-566 ◽  
Author(s):  
Louise Delaigue ◽  
Helmuth Thomas ◽  
Alfonso Mucci
Keyword(s):  
Surface Waters ◽  
Brackish Water ◽  
Field Measurements ◽  
Mixing Model ◽  
Isotopic Tracers ◽  
Lawrence Estuary ◽  
Relative Contribution ◽  
Saguenay Fjord ◽  
Spring Freshet ◽  
St Lawrence Estuary

Abstract. The Saguenay Fjord is a major tributary of the St. Lawrence Estuary and is strongly stratified. A 6–8 m wedge of brackish water typically overlies up to 270 m of seawater. Relative to the St. Lawrence River, the surface waters of the Saguenay Fjord are less alkaline and host higher dissolved organic carbon (DOC) concentrations. In view of the latter, surface waters of the fjord are expected to be a net source of CO2 to the atmosphere, as they partly originate from the flushing of organic-rich soil porewaters. Nonetheless, the CO2 dynamics in the fjord are modulated with the rising tide by the intrusion, at the surface, of brackish water from the Upper St. Lawrence Estuary, as well as an overflow of mixed seawater over the shallow sill from the Lower St. Lawrence Estuary. Using geochemical and isotopic tracers, in combination with an optimization multiparameter algorithm (OMP), we determined the relative contribution of known source waters to the water column in the Saguenay Fjord, including waters that originate from the Lower St. Lawrence Estuary and replenish the fjord's deep basins. These results, when included in a conservative mixing model and compared to field measurements, serve to identify the dominant factors, other than physical mixing, such as biological activity (photosynthesis, respiration) and gas exchange at the air–water interface, that impact the water properties (e.g., pH, pCO2) of the fjord. Results indicate that the fjord's surface waters are a net source of CO2 to the atmosphere during periods of high freshwater discharge (e.g., spring freshet), whereas they serve as a net sink of atmospheric CO2 when their practical salinity exceeds ∼5–10.

Deepwater Exchange Processes in the Saguenay Fjord

1979 ◽  
Vol 36 (1) ◽  
pp. 42-53 ◽  
Author(s):  
G. H. Seibert ◽  
R. W. Trites ◽  
S. J. Reid
Keyword(s):  
Deep Basin ◽  
Lawrence Estuary ◽  
Deep Waters ◽  
Saguenay Fjord ◽  
Exchange Processes ◽  
Density Flow ◽  
Sill Depth ◽  
Flushing Rates ◽  
St Lawrence Estuary ◽  
Outer Basin

Evidence is presented showing that the deep waters in the Saguenay Fjord are flushed at a rate that appears to be significantly higher than other sill fjords with comparable bathymetry. Interval waves in the St. Lawrence estuary, with magnitudes of up to 60 m, provide a mechanism for bringing up dense water, semidiurnally, to the level of the seaward sill. Providing the density of the deep water in the fjord's outer basin is less than that at sill depth, a density flow develops and descends into the basin. Estimates of volume and kinetic energy fluxes of the plume suggest that, by itself, this is insufficient to explain the high flushing rates observed. Other processes, such as internal waves, which must be operative in carrying energy into the deep basin, are discussed. Key words: estuaries, sill fjords, mixing, circulation, coastal

Mercury speciation in the Lower St. Lawrence Estuary

2000 ◽  
Vol 57 (S1) ◽  
pp. 138-147 ◽  
Author(s):  
Daniel Cossa ◽  
Charles Gobeil
Keyword(s):  
Water Column ◽  
Surface Waters ◽  
Feeding Habits ◽  
Mercury Speciation ◽  
Estuarine Sediments ◽  
Sediment Surface ◽  
Pore Waters ◽  
Mass Balance Calculation ◽  
Lawrence Estuary ◽  
St Lawrence Estuary

Mercury speciation was determined in the water column and sediment pore waters of the Lower St. Lawrence Estuary, and total Hg (HgT) was measured in seven biological species, including pelagic and demersal fish and crustaceans. In water, HgT concentrations ranged from 1.8 to 7.8 pM, with the highest levels in surface waters and the lowest in deep waters (1.8-2.9 pM). HgT concentrations in sediment pore waters were 10 times as high, with methyl mercury levels of 5.1-14.4 pM. Reactive Hg (HgR) generally accounted for around 20% of HgT in the water column and <30% in pore waters. The distribution of elemental Hg and HgR suggests that Hg(II) is reduced in surface waters and that inorganic Hg is mobilized during remineralization of organic matter at the sediment surface. In the biota, concentrations ranged between 0.05 and 0.89 nmol·g-1 (wet weight). Feeding habits and habitats account for these observations. Results suggest that the sediment is the main source of Hg contamination for the biota. A mass balance calculation showed that the Hg flux entering the lower estuary from the St. Lawrence River is equivalent to the amount buried in estuarine sediments.

Survey of Trace Metal Contents of Suspended Matter in the St. Lawrence Estuary and Saguenay Fjord

1978 ◽  
Vol 35 (3) ◽  
pp. 338-345 ◽  
Author(s):  
D. Cossa ◽  
S. A. Poulet
Keyword(s):  
Trace Elements ◽  
Trace Metal ◽  
Surface Waters ◽  
Suspended Matter ◽  
Lawrence Estuary ◽  
Manganese Zinc ◽  
Saguenay Fjord ◽  
Metal Contents ◽  
The Rich ◽  
St Lawrence Estuary

Trace metal contents (Mn, Zn, Pb, and Cd) of suspended particulate matter were measured in the upper St. Lawrence estuary and Saguenay fjord. In the estuary, elution of the trace metal fraction adsorbed on particles seems to be mostly responsible for the significant differences in concentrations observed at the freshwater–saltwater boundary. In the Saguenay fjord, particles from deep waters are enriched with trace metals, especially Mn, compared with those from surface waters. This enrichment is probably due to Mn oxidation and simultaneous scavenging of the other trace elements. High Pb and Cd levels in particles of surface waters of the fjord seem to depend mostly on their high affinity for the rich organic matter. Key words: trace elements, suspended matter, estuaries, manganese, zinc, lead, cadmium

Penetration of the Deep Layer of the Saguenay Fjord by Surface Waters of the St. Lawrence Estuary

1975 ◽  
Vol 32 (12) ◽  
pp. 2373-2377 ◽  
Author(s):  
Jean Claude Therriault ◽  
Guy Lacroix
Keyword(s):  
Surface Water ◽  
Deep Water ◽  
Surface Waters ◽  
Deep Layer ◽  
Physicochemical Characteristics ◽  
Estuarine Water ◽  
Lawrence Estuary ◽  
Saguenay Fjord ◽  
Summer Warming ◽  
St Lawrence Estuary

A strong similarity is demonstrated in summertime physicochemical characteristics between the deep water of the Saguenay fjord and the surface water of the St. Lawrence estuary. Summer warming of the deep layer of the Saguenay is progressive from the mouth towards the head of the fjord. The mechanism proposed is the penetration of surface estuarine water over the shallow sill during the rising tide. The abnormally high chlorophyll values in this deep layer may be explained by the same advective mechanism.

scholarly journals Response of the Lower St. Lawrence Estuary to External Forcing in Winter

2006 ◽  
Vol 36 (8) ◽  
pp. 1485-1501 ◽  
Author(s):  
G. C. Smith ◽  
F. J. Saucier ◽  
D. Straub
Keyword(s):  
Low Frequency ◽  
Internal Tides ◽  
Surface Mixed Layer ◽  
Cold Intermediate Layer ◽  
Lawrence Estuary ◽  
Surface Stability ◽  
Tidal Streams ◽  
Harmonic Analyses ◽  
St Lawrence Estuary

Abstract Mostly because of a lack of observations, fundamental aspects of the St. Lawrence Estuary’s wintertime response to forcing remain poorly understood. The results of a field campaign over the winter of 2002/03 in the estuary are presented. The response of the system to tidal forcing is assessed through the use of harmonic analyses of temperature, salinity, sea level, and current observations. The analyses confirm previous evidence for the presence of semidiurnal internal tides, albeit at greater depths than previously observed for ice-free months. The low-frequency tidal streams were found to be mostly baroclinic in character and to produce an important neap tide intensification of the estuarine circulation. Despite stronger atmospheric momentum forcing in winter, the response is found to be less coherent with the winds than seen in previous studies of ice-free months. The tidal residuals show the cold intermediate layer in the estuary is renewed rapidly (14 days) in late March by the advection of a wedge of near-freezing waters from the Gulf of St. Lawrence. In situ processes appeared to play a lesser role in the renewal of this layer. In particular, significant wintertime deepening of the estuarine surface mixed layer was prevented by surface stability, which remained high throughout the winter. The observations also suggest that the bottom circulation was intensified during winter, with the intrusion in the deep layer of relatively warm Atlantic waters, such that the 3°C isotherm rose from below 150 m to near 60 m.

scholarly journals Spatial variations of CO<sub>2</sub> fluxes in the Saguenay Fjord (Québec, Canada) and results of a water mixing model

2019 ◽  
Author(s):  
Louise Delaigue ◽  
Helmuth Thomas ◽  
Alfonso Mucci
Keyword(s):  
Surface Waters ◽  
Brackish Water ◽  
Field Measurements ◽  
Mixing Model ◽  
Isotopic Tracers ◽  
Lawrence Estuary ◽  
Relative Contribution ◽  
Saguenay Fjord ◽  
Spring Freshet ◽  
St Lawrence Estuary

Abstract. The Saguenay Fjord is a major tributary of the St. Lawrence Estuary and is strongly stratified. A 6–8 m wedge of brackish water typically overlies up to 270 m of seawater. Relative to the St. Lawrence River, the surface waters of the Saguenay Fjord are less alkaline and host higher dissolved organic carbon (DOC) concentrations. In view of the latter, surface waters of the fjord are expected to be a net source of CO2 to the atmosphere, as they partly originate from the flushing of organic-rich soil porewaters. Nonetheless, the intrusion, at the surface, of brackish water from the upper estuary with the rising tide, as well as mixing of seawater, overflowing the sill from the lower estuary, modulate the CO2 dynamics in the fjord. Using geochemical and isotopic tracers, in combination with an optimization multiparameter algorithm (OMP), we determined the relative contribution of known source-waters to the water column in the Saguenay Fjord, including waters that originate from the Lower St. Lawrence Estuary and replenish the fjord’s deep basins. These results, when combined to a conservative mixing model and compared to field measurements, serve to identify the dominant factors, other than physical mixing, such as biological activity (photosynthesis, respiration) and gas exchange at the air-water interface, that impact the water properties (e.g., pH, pCO2) of the fjord. Results indicate that the fjord’s surface waters are a net source of CO2 to the atmosphere during periods of high freshwater discharge (e.g., spring freshet) whereas they serve as a net sink of atmospheric CO2 when their practical salinity exceeds ~ 5–10.

scholarly journals Tidally induced variations of pH at the head of the Laurentian Channel

2018 ◽  
Vol 75 (7) ◽  
pp. 1128-1141 ◽  
Author(s):  
Alfonso Mucci ◽  
Maurice Levasseur ◽  
Yves Gratton ◽  
Chloé Martias ◽  
Michael Scarratt ◽  
...  
Keyword(s):  
Water Column ◽  
Surface Waters ◽  
Field Measurements ◽  
Tidal Mixing ◽  
Lawrence Estuary ◽  
Saguenay Fjord ◽  
Physical And Chemical Variables ◽  
The Difference ◽  
St Lawrence Estuary ◽  
The Impact

The head of the Laurentian Channel is a very dynamic region of exceptional biological richness. To evaluate the impact of freshwater discharge, tidal mixing, and biological activity on the pH of surface waters in this region, a suite of physical and chemical variables was measured throughout the water column over two tidal cycles. The relative contributions to the water column of the four source-water types that converge in this region were evaluated using an optimum multiparameter algorithm (OMP). Results of the OMP analysis were used to reconstruct the water column properties assuming conservative mixing, and the difference between the model properties and field measurements served to identify factors that control the pH of the surface waters. These surface waters are generally undersaturated with respect to aragonite, mostly due to the intrusion of waters from the Upper St. Lawrence Estuary and the Saguenay Fjord. The presence of a cold intermediate layer impedes the upwelling of the deeper, hypoxic, lower pH and aragonite-undersaturated waters of the Lower St. Lawrence Estuary to depths shallower than 50 m.

Variability of the circulation in the western North Atlantic and its impact on deep-water oxygen concentrations in the St. Lawrence Estuary on the western continental shelf: evidence from observations

2021 ◽  
Author(s):  
Mathilde Jutras ◽  
Carolina Dufour ◽  
Alfonso Mucci ◽  
Frédéric Cyr ◽  
Denis Gilbert
Keyword(s):  
Continental Shelf ◽  
North Atlantic ◽  
Gulf Stream ◽  
Scotian Shelf ◽  
Lawrence Estuary ◽  
The North ◽  
Deep Waters ◽  
Labrador Current ◽  
The North Atlantic ◽  
St Lawrence Estuary

&lt;p&gt;Oxygen concentrations in the deep waters of the Lower St. Lawrence Estuary, in eastern Canada, have decreased by 50% over the past century, reaching hypoxic levels. To study the causes of this deoxygenation, we applied a mixing model (an extended multi-parameter analysis - eOMP) to data collected in the St. Lawrence Estuary since the 1970s and from the late 1990s to 2018. This method accounts for diapycnal mixing and can distinguish between the physical and biogeochemical causes of deoxygenation. The eOMP reveals that, in recent years, most of the deoxygenation of deep waters of the St. Lawrence Estuary is due to a change in the circulation pattern in the western North Atlantic. Since 2008, the Slope Sea and the deep waters of the St. Lawrence Estuary are fed by an increasing amount of oxygen-poor North Atlantic Central Waters (NACW), transported by the Gulf Stream, at the expense of oxygen-rich Labrador Current Waters (LCW). The oxygenation level of the St. Lawrence Estuary therefore reflects what is happening in the western North Atlantic. In contrast, the eOMP shows that, from the 1970s to the late 1990s, biogeochemical changes such as local eutrophication and variations in oxygen consumption rates in the North Atlantic dominated the deoxygenation.&amp;#160;&lt;/p&gt;&lt;p&gt;Further analyses suggest that the variability in the LCW:NACW ratio in the Slope Waters is mainly controlled by the Scotian Shelf-break Current, an extension of the Labrador Current, and not by the position or strength of the Gulf Stream, as often suggested. When the Labrador Current is strong, little of the southward flowing Labrador Current waters follow the coast all the way to the Scotian Shelf, and most of these waters are deviated east towards the North Atlantic. The opposite is true when the Labrador Current is weak. We will present some analysis of LCW trajectories in different conditions and discuss their potential drivers, based on a high resolution model. Overall, our results highlight the primary role of the Labrador Current in determining (i) the oxygen concentration and other water properties on the western North Atlantic continental shelf and slope, and (ii) the advection of fresh Labrador Current Water into the subpolar North Atlantic, with possible implications on the thermohaline and gyre circulation.&lt;/p&gt;

New distribution and host record for the starfish parasite Dendrogaster (Crustacea: Ascothoracida)

1994 ◽  
Vol 74 (2) ◽  
pp. 419-425 ◽  
Author(s):  
Jean-François Hamel ◽  
Annie Mercier
Keyword(s):  
Vascular System ◽  
Negative Impact ◽  
Host Record ◽  
Eastern Canada ◽  
The West ◽  
Lawrence Estuary ◽  
Deep Waters ◽  
St Lawrence Estuary ◽  
First Time ◽  
New Distribution

This work presents the description of an intracoelomic parasite of the genus Dendrogaster (Crustacea: Ascothoracida), the largest ever reported, collected for the first time from the starfish Hippasteria phrygiana in the deep waters of the St Lawrence Estuary (eastern Canada). The parasite bears a close resemblance to only one previously described species, D. arbusculus from the west American coast, suggesting a bicoastal and possibly circumpolar distribution. Female growth is concurrent with embryo development and the parasite may have a negative impact on host starfish densities through gonad atrophy. This research also demystifies the old and persistent description of a supposed parasite in H. phrygiana 70 years ago, Laocoön paradoxus, and finally concludes that this parasite never existed and in fact represents the water vascular system found in all starfish.

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